1 //===- CostModel.cpp ------ Cost Model Analysis ---------------------------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file defines the cost model analysis. It provides a very basic cost
11 // estimation for LLVM-IR. This analysis uses the services of the codegen
12 // to approximate the cost of any IR instruction when lowered to machine
13 // instructions. The cost results are unit-less and the cost number represents
14 // the throughput of the machine assuming that all loads hit the cache, all
15 // branches are predicted, etc. The cost numbers can be added in order to
16 // compare two or more transformation alternatives.
17 //
18 //===----------------------------------------------------------------------===//
19
20 #include "llvm/ADT/STLExtras.h"
21 #include "llvm/Analysis/Passes.h"
22 #include "llvm/Analysis/TargetTransformInfo.h"
23 #include "llvm/IR/Function.h"
24 #include "llvm/IR/Instructions.h"
25 #include "llvm/IR/IntrinsicInst.h"
26 #include "llvm/IR/Value.h"
27 #include "llvm/Pass.h"
28 #include "llvm/Support/CommandLine.h"
29 #include "llvm/Support/Debug.h"
30 #include "llvm/Support/raw_ostream.h"
31 using namespace llvm;
32
33 #define CM_NAME "cost-model"
34 #define DEBUG_TYPE CM_NAME
35
36 static cl::opt<bool> EnableReduxCost("costmodel-reduxcost", cl::init(false),
37 cl::Hidden,
38 cl::desc("Recognize reduction patterns."));
39
40 namespace {
41 class CostModelAnalysis : public FunctionPass {
42
43 public:
44 static char ID; // Class identification, replacement for typeinfo
CostModelAnalysis()45 CostModelAnalysis() : FunctionPass(ID), F(nullptr), TTI(nullptr) {
46 initializeCostModelAnalysisPass(
47 *PassRegistry::getPassRegistry());
48 }
49
50 /// Returns the expected cost of the instruction.
51 /// Returns -1 if the cost is unknown.
52 /// Note, this method does not cache the cost calculation and it
53 /// can be expensive in some cases.
54 unsigned getInstructionCost(const Instruction *I) const;
55
56 private:
57 void getAnalysisUsage(AnalysisUsage &AU) const override;
58 bool runOnFunction(Function &F) override;
59 void print(raw_ostream &OS, const Module*) const override;
60
61 /// The function that we analyze.
62 Function *F;
63 /// Target information.
64 const TargetTransformInfo *TTI;
65 };
66 } // End of anonymous namespace
67
68 // Register this pass.
69 char CostModelAnalysis::ID = 0;
70 static const char cm_name[] = "Cost Model Analysis";
INITIALIZE_PASS_BEGIN(CostModelAnalysis,CM_NAME,cm_name,false,true)71 INITIALIZE_PASS_BEGIN(CostModelAnalysis, CM_NAME, cm_name, false, true)
72 INITIALIZE_PASS_END (CostModelAnalysis, CM_NAME, cm_name, false, true)
73
74 FunctionPass *llvm::createCostModelAnalysisPass() {
75 return new CostModelAnalysis();
76 }
77
78 void
getAnalysisUsage(AnalysisUsage & AU) const79 CostModelAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
80 AU.setPreservesAll();
81 }
82
83 bool
runOnFunction(Function & F)84 CostModelAnalysis::runOnFunction(Function &F) {
85 this->F = &F;
86 TTI = getAnalysisIfAvailable<TargetTransformInfo>();
87
88 return false;
89 }
90
isReverseVectorMask(SmallVectorImpl<int> & Mask)91 static bool isReverseVectorMask(SmallVectorImpl<int> &Mask) {
92 for (unsigned i = 0, MaskSize = Mask.size(); i < MaskSize; ++i)
93 if (Mask[i] > 0 && Mask[i] != (int)(MaskSize - 1 - i))
94 return false;
95 return true;
96 }
97
isAlternateVectorMask(SmallVectorImpl<int> & Mask)98 static bool isAlternateVectorMask(SmallVectorImpl<int> &Mask) {
99 bool isAlternate = true;
100 unsigned MaskSize = Mask.size();
101
102 // Example: shufflevector A, B, <0,5,2,7>
103 for (unsigned i = 0; i < MaskSize && isAlternate; ++i) {
104 if (Mask[i] < 0)
105 continue;
106 isAlternate = Mask[i] == (int)((i & 1) ? MaskSize + i : i);
107 }
108
109 if (isAlternate)
110 return true;
111
112 isAlternate = true;
113 // Example: shufflevector A, B, <4,1,6,3>
114 for (unsigned i = 0; i < MaskSize && isAlternate; ++i) {
115 if (Mask[i] < 0)
116 continue;
117 isAlternate = Mask[i] == (int)((i & 1) ? i : MaskSize + i);
118 }
119
120 return isAlternate;
121 }
122
getOperandInfo(Value * V)123 static TargetTransformInfo::OperandValueKind getOperandInfo(Value *V) {
124 TargetTransformInfo::OperandValueKind OpInfo =
125 TargetTransformInfo::OK_AnyValue;
126
127 // Check for a splat of a constant or for a non uniform vector of constants.
128 if (isa<ConstantVector>(V) || isa<ConstantDataVector>(V)) {
129 OpInfo = TargetTransformInfo::OK_NonUniformConstantValue;
130 if (cast<Constant>(V)->getSplatValue() != nullptr)
131 OpInfo = TargetTransformInfo::OK_UniformConstantValue;
132 }
133
134 return OpInfo;
135 }
136
matchPairwiseShuffleMask(ShuffleVectorInst * SI,bool IsLeft,unsigned Level)137 static bool matchPairwiseShuffleMask(ShuffleVectorInst *SI, bool IsLeft,
138 unsigned Level) {
139 // We don't need a shuffle if we just want to have element 0 in position 0 of
140 // the vector.
141 if (!SI && Level == 0 && IsLeft)
142 return true;
143 else if (!SI)
144 return false;
145
146 SmallVector<int, 32> Mask(SI->getType()->getVectorNumElements(), -1);
147
148 // Build a mask of 0, 2, ... (left) or 1, 3, ... (right) depending on whether
149 // we look at the left or right side.
150 for (unsigned i = 0, e = (1 << Level), val = !IsLeft; i != e; ++i, val += 2)
151 Mask[i] = val;
152
153 SmallVector<int, 16> ActualMask = SI->getShuffleMask();
154 if (Mask != ActualMask)
155 return false;
156
157 return true;
158 }
159
matchPairwiseReductionAtLevel(const BinaryOperator * BinOp,unsigned Level,unsigned NumLevels)160 static bool matchPairwiseReductionAtLevel(const BinaryOperator *BinOp,
161 unsigned Level, unsigned NumLevels) {
162 // Match one level of pairwise operations.
163 // %rdx.shuf.0.0 = shufflevector <4 x float> %rdx, <4 x float> undef,
164 // <4 x i32> <i32 0, i32 2 , i32 undef, i32 undef>
165 // %rdx.shuf.0.1 = shufflevector <4 x float> %rdx, <4 x float> undef,
166 // <4 x i32> <i32 1, i32 3, i32 undef, i32 undef>
167 // %bin.rdx.0 = fadd <4 x float> %rdx.shuf.0.0, %rdx.shuf.0.1
168 if (BinOp == nullptr)
169 return false;
170
171 assert(BinOp->getType()->isVectorTy() && "Expecting a vector type");
172
173 unsigned Opcode = BinOp->getOpcode();
174 Value *L = BinOp->getOperand(0);
175 Value *R = BinOp->getOperand(1);
176
177 ShuffleVectorInst *LS = dyn_cast<ShuffleVectorInst>(L);
178 if (!LS && Level)
179 return false;
180 ShuffleVectorInst *RS = dyn_cast<ShuffleVectorInst>(R);
181 if (!RS && Level)
182 return false;
183
184 // On level 0 we can omit one shufflevector instruction.
185 if (!Level && !RS && !LS)
186 return false;
187
188 // Shuffle inputs must match.
189 Value *NextLevelOpL = LS ? LS->getOperand(0) : nullptr;
190 Value *NextLevelOpR = RS ? RS->getOperand(0) : nullptr;
191 Value *NextLevelOp = nullptr;
192 if (NextLevelOpR && NextLevelOpL) {
193 // If we have two shuffles their operands must match.
194 if (NextLevelOpL != NextLevelOpR)
195 return false;
196
197 NextLevelOp = NextLevelOpL;
198 } else if (Level == 0 && (NextLevelOpR || NextLevelOpL)) {
199 // On the first level we can omit the shufflevector <0, undef,...>. So the
200 // input to the other shufflevector <1, undef> must match with one of the
201 // inputs to the current binary operation.
202 // Example:
203 // %NextLevelOpL = shufflevector %R, <1, undef ...>
204 // %BinOp = fadd %NextLevelOpL, %R
205 if (NextLevelOpL && NextLevelOpL != R)
206 return false;
207 else if (NextLevelOpR && NextLevelOpR != L)
208 return false;
209
210 NextLevelOp = NextLevelOpL ? R : L;
211 } else
212 return false;
213
214 // Check that the next levels binary operation exists and matches with the
215 // current one.
216 BinaryOperator *NextLevelBinOp = nullptr;
217 if (Level + 1 != NumLevels) {
218 if (!(NextLevelBinOp = dyn_cast<BinaryOperator>(NextLevelOp)))
219 return false;
220 else if (NextLevelBinOp->getOpcode() != Opcode)
221 return false;
222 }
223
224 // Shuffle mask for pairwise operation must match.
225 if (matchPairwiseShuffleMask(LS, true, Level)) {
226 if (!matchPairwiseShuffleMask(RS, false, Level))
227 return false;
228 } else if (matchPairwiseShuffleMask(RS, true, Level)) {
229 if (!matchPairwiseShuffleMask(LS, false, Level))
230 return false;
231 } else
232 return false;
233
234 if (++Level == NumLevels)
235 return true;
236
237 // Match next level.
238 return matchPairwiseReductionAtLevel(NextLevelBinOp, Level, NumLevels);
239 }
240
matchPairwiseReduction(const ExtractElementInst * ReduxRoot,unsigned & Opcode,Type * & Ty)241 static bool matchPairwiseReduction(const ExtractElementInst *ReduxRoot,
242 unsigned &Opcode, Type *&Ty) {
243 if (!EnableReduxCost)
244 return false;
245
246 // Need to extract the first element.
247 ConstantInt *CI = dyn_cast<ConstantInt>(ReduxRoot->getOperand(1));
248 unsigned Idx = ~0u;
249 if (CI)
250 Idx = CI->getZExtValue();
251 if (Idx != 0)
252 return false;
253
254 BinaryOperator *RdxStart = dyn_cast<BinaryOperator>(ReduxRoot->getOperand(0));
255 if (!RdxStart)
256 return false;
257
258 Type *VecTy = ReduxRoot->getOperand(0)->getType();
259 unsigned NumVecElems = VecTy->getVectorNumElements();
260 if (!isPowerOf2_32(NumVecElems))
261 return false;
262
263 // We look for a sequence of shuffle,shuffle,add triples like the following
264 // that builds a pairwise reduction tree.
265 //
266 // (X0, X1, X2, X3)
267 // (X0 + X1, X2 + X3, undef, undef)
268 // ((X0 + X1) + (X2 + X3), undef, undef, undef)
269 //
270 // %rdx.shuf.0.0 = shufflevector <4 x float> %rdx, <4 x float> undef,
271 // <4 x i32> <i32 0, i32 2 , i32 undef, i32 undef>
272 // %rdx.shuf.0.1 = shufflevector <4 x float> %rdx, <4 x float> undef,
273 // <4 x i32> <i32 1, i32 3, i32 undef, i32 undef>
274 // %bin.rdx.0 = fadd <4 x float> %rdx.shuf.0.0, %rdx.shuf.0.1
275 // %rdx.shuf.1.0 = shufflevector <4 x float> %bin.rdx.0, <4 x float> undef,
276 // <4 x i32> <i32 0, i32 undef, i32 undef, i32 undef>
277 // %rdx.shuf.1.1 = shufflevector <4 x float> %bin.rdx.0, <4 x float> undef,
278 // <4 x i32> <i32 1, i32 undef, i32 undef, i32 undef>
279 // %bin.rdx8 = fadd <4 x float> %rdx.shuf.1.0, %rdx.shuf.1.1
280 // %r = extractelement <4 x float> %bin.rdx8, i32 0
281 if (!matchPairwiseReductionAtLevel(RdxStart, 0, Log2_32(NumVecElems)))
282 return false;
283
284 Opcode = RdxStart->getOpcode();
285 Ty = VecTy;
286
287 return true;
288 }
289
290 static std::pair<Value *, ShuffleVectorInst *>
getShuffleAndOtherOprd(BinaryOperator * B)291 getShuffleAndOtherOprd(BinaryOperator *B) {
292
293 Value *L = B->getOperand(0);
294 Value *R = B->getOperand(1);
295 ShuffleVectorInst *S = nullptr;
296
297 if ((S = dyn_cast<ShuffleVectorInst>(L)))
298 return std::make_pair(R, S);
299
300 S = dyn_cast<ShuffleVectorInst>(R);
301 return std::make_pair(L, S);
302 }
303
matchVectorSplittingReduction(const ExtractElementInst * ReduxRoot,unsigned & Opcode,Type * & Ty)304 static bool matchVectorSplittingReduction(const ExtractElementInst *ReduxRoot,
305 unsigned &Opcode, Type *&Ty) {
306 if (!EnableReduxCost)
307 return false;
308
309 // Need to extract the first element.
310 ConstantInt *CI = dyn_cast<ConstantInt>(ReduxRoot->getOperand(1));
311 unsigned Idx = ~0u;
312 if (CI)
313 Idx = CI->getZExtValue();
314 if (Idx != 0)
315 return false;
316
317 BinaryOperator *RdxStart = dyn_cast<BinaryOperator>(ReduxRoot->getOperand(0));
318 if (!RdxStart)
319 return false;
320 unsigned RdxOpcode = RdxStart->getOpcode();
321
322 Type *VecTy = ReduxRoot->getOperand(0)->getType();
323 unsigned NumVecElems = VecTy->getVectorNumElements();
324 if (!isPowerOf2_32(NumVecElems))
325 return false;
326
327 // We look for a sequence of shuffles and adds like the following matching one
328 // fadd, shuffle vector pair at a time.
329 //
330 // %rdx.shuf = shufflevector <4 x float> %rdx, <4 x float> undef,
331 // <4 x i32> <i32 2, i32 3, i32 undef, i32 undef>
332 // %bin.rdx = fadd <4 x float> %rdx, %rdx.shuf
333 // %rdx.shuf7 = shufflevector <4 x float> %bin.rdx, <4 x float> undef,
334 // <4 x i32> <i32 1, i32 undef, i32 undef, i32 undef>
335 // %bin.rdx8 = fadd <4 x float> %bin.rdx, %rdx.shuf7
336 // %r = extractelement <4 x float> %bin.rdx8, i32 0
337
338 unsigned MaskStart = 1;
339 Value *RdxOp = RdxStart;
340 SmallVector<int, 32> ShuffleMask(NumVecElems, 0);
341 unsigned NumVecElemsRemain = NumVecElems;
342 while (NumVecElemsRemain - 1) {
343 // Check for the right reduction operation.
344 BinaryOperator *BinOp;
345 if (!(BinOp = dyn_cast<BinaryOperator>(RdxOp)))
346 return false;
347 if (BinOp->getOpcode() != RdxOpcode)
348 return false;
349
350 Value *NextRdxOp;
351 ShuffleVectorInst *Shuffle;
352 std::tie(NextRdxOp, Shuffle) = getShuffleAndOtherOprd(BinOp);
353
354 // Check the current reduction operation and the shuffle use the same value.
355 if (Shuffle == nullptr)
356 return false;
357 if (Shuffle->getOperand(0) != NextRdxOp)
358 return false;
359
360 // Check that shuffle masks matches.
361 for (unsigned j = 0; j != MaskStart; ++j)
362 ShuffleMask[j] = MaskStart + j;
363 // Fill the rest of the mask with -1 for undef.
364 std::fill(&ShuffleMask[MaskStart], ShuffleMask.end(), -1);
365
366 SmallVector<int, 16> Mask = Shuffle->getShuffleMask();
367 if (ShuffleMask != Mask)
368 return false;
369
370 RdxOp = NextRdxOp;
371 NumVecElemsRemain /= 2;
372 MaskStart *= 2;
373 }
374
375 Opcode = RdxOpcode;
376 Ty = VecTy;
377 return true;
378 }
379
getInstructionCost(const Instruction * I) const380 unsigned CostModelAnalysis::getInstructionCost(const Instruction *I) const {
381 if (!TTI)
382 return -1;
383
384 switch (I->getOpcode()) {
385 case Instruction::GetElementPtr:{
386 Type *ValTy = I->getOperand(0)->getType()->getPointerElementType();
387 return TTI->getAddressComputationCost(ValTy);
388 }
389
390 case Instruction::Ret:
391 case Instruction::PHI:
392 case Instruction::Br: {
393 return TTI->getCFInstrCost(I->getOpcode());
394 }
395 case Instruction::Add:
396 case Instruction::FAdd:
397 case Instruction::Sub:
398 case Instruction::FSub:
399 case Instruction::Mul:
400 case Instruction::FMul:
401 case Instruction::UDiv:
402 case Instruction::SDiv:
403 case Instruction::FDiv:
404 case Instruction::URem:
405 case Instruction::SRem:
406 case Instruction::FRem:
407 case Instruction::Shl:
408 case Instruction::LShr:
409 case Instruction::AShr:
410 case Instruction::And:
411 case Instruction::Or:
412 case Instruction::Xor: {
413 TargetTransformInfo::OperandValueKind Op1VK =
414 getOperandInfo(I->getOperand(0));
415 TargetTransformInfo::OperandValueKind Op2VK =
416 getOperandInfo(I->getOperand(1));
417 return TTI->getArithmeticInstrCost(I->getOpcode(), I->getType(), Op1VK,
418 Op2VK);
419 }
420 case Instruction::Select: {
421 const SelectInst *SI = cast<SelectInst>(I);
422 Type *CondTy = SI->getCondition()->getType();
423 return TTI->getCmpSelInstrCost(I->getOpcode(), I->getType(), CondTy);
424 }
425 case Instruction::ICmp:
426 case Instruction::FCmp: {
427 Type *ValTy = I->getOperand(0)->getType();
428 return TTI->getCmpSelInstrCost(I->getOpcode(), ValTy);
429 }
430 case Instruction::Store: {
431 const StoreInst *SI = cast<StoreInst>(I);
432 Type *ValTy = SI->getValueOperand()->getType();
433 return TTI->getMemoryOpCost(I->getOpcode(), ValTy,
434 SI->getAlignment(),
435 SI->getPointerAddressSpace());
436 }
437 case Instruction::Load: {
438 const LoadInst *LI = cast<LoadInst>(I);
439 return TTI->getMemoryOpCost(I->getOpcode(), I->getType(),
440 LI->getAlignment(),
441 LI->getPointerAddressSpace());
442 }
443 case Instruction::ZExt:
444 case Instruction::SExt:
445 case Instruction::FPToUI:
446 case Instruction::FPToSI:
447 case Instruction::FPExt:
448 case Instruction::PtrToInt:
449 case Instruction::IntToPtr:
450 case Instruction::SIToFP:
451 case Instruction::UIToFP:
452 case Instruction::Trunc:
453 case Instruction::FPTrunc:
454 case Instruction::BitCast:
455 case Instruction::AddrSpaceCast: {
456 Type *SrcTy = I->getOperand(0)->getType();
457 return TTI->getCastInstrCost(I->getOpcode(), I->getType(), SrcTy);
458 }
459 case Instruction::ExtractElement: {
460 const ExtractElementInst * EEI = cast<ExtractElementInst>(I);
461 ConstantInt *CI = dyn_cast<ConstantInt>(I->getOperand(1));
462 unsigned Idx = -1;
463 if (CI)
464 Idx = CI->getZExtValue();
465
466 // Try to match a reduction sequence (series of shufflevector and vector
467 // adds followed by a extractelement).
468 unsigned ReduxOpCode;
469 Type *ReduxType;
470
471 if (matchVectorSplittingReduction(EEI, ReduxOpCode, ReduxType))
472 return TTI->getReductionCost(ReduxOpCode, ReduxType, false);
473 else if (matchPairwiseReduction(EEI, ReduxOpCode, ReduxType))
474 return TTI->getReductionCost(ReduxOpCode, ReduxType, true);
475
476 return TTI->getVectorInstrCost(I->getOpcode(),
477 EEI->getOperand(0)->getType(), Idx);
478 }
479 case Instruction::InsertElement: {
480 const InsertElementInst * IE = cast<InsertElementInst>(I);
481 ConstantInt *CI = dyn_cast<ConstantInt>(IE->getOperand(2));
482 unsigned Idx = -1;
483 if (CI)
484 Idx = CI->getZExtValue();
485 return TTI->getVectorInstrCost(I->getOpcode(),
486 IE->getType(), Idx);
487 }
488 case Instruction::ShuffleVector: {
489 const ShuffleVectorInst *Shuffle = cast<ShuffleVectorInst>(I);
490 Type *VecTypOp0 = Shuffle->getOperand(0)->getType();
491 unsigned NumVecElems = VecTypOp0->getVectorNumElements();
492 SmallVector<int, 16> Mask = Shuffle->getShuffleMask();
493
494 if (NumVecElems == Mask.size()) {
495 if (isReverseVectorMask(Mask))
496 return TTI->getShuffleCost(TargetTransformInfo::SK_Reverse, VecTypOp0,
497 0, nullptr);
498 if (isAlternateVectorMask(Mask))
499 return TTI->getShuffleCost(TargetTransformInfo::SK_Alternate,
500 VecTypOp0, 0, nullptr);
501 }
502
503 return -1;
504 }
505 case Instruction::Call:
506 if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
507 SmallVector<Type*, 4> Tys;
508 for (unsigned J = 0, JE = II->getNumArgOperands(); J != JE; ++J)
509 Tys.push_back(II->getArgOperand(J)->getType());
510
511 return TTI->getIntrinsicInstrCost(II->getIntrinsicID(), II->getType(),
512 Tys);
513 }
514 return -1;
515 default:
516 // We don't have any information on this instruction.
517 return -1;
518 }
519 }
520
print(raw_ostream & OS,const Module *) const521 void CostModelAnalysis::print(raw_ostream &OS, const Module*) const {
522 if (!F)
523 return;
524
525 for (Function::iterator B = F->begin(), BE = F->end(); B != BE; ++B) {
526 for (BasicBlock::iterator it = B->begin(), e = B->end(); it != e; ++it) {
527 Instruction *Inst = it;
528 unsigned Cost = getInstructionCost(Inst);
529 if (Cost != (unsigned)-1)
530 OS << "Cost Model: Found an estimated cost of " << Cost;
531 else
532 OS << "Cost Model: Unknown cost";
533
534 OS << " for instruction: "<< *Inst << "\n";
535 }
536 }
537 }
538